Help a novice

[JoeMorris]

Hi,

I'll set my stall out right away - I've built quite a lot of DIY electronics, mainly effects, but I know absolutely nothing about the world of tube amps.
I'm not a guitarist, I'm a keyboard playing synth man.

If that doesn't get me ran out of town, I was hoping for some advice.

I'd love to build a custom combo tube amp for my keyboards so I can run them through some nicevalve heat and get them pushing some real air for micing up purposes and an injection of real life.

As I say, I don't know where to start really. Doesn't need to be super loud, but big enough to capture some low end. Looking to build my own cabinet etc.

Any pointers?

[oldhousescott]

Well, the first caveat for anyone just starting out in building tube equipment is that there are potentially lethal voltages inside, so safety first, last, and always.

Going from back to front, I would say you need at least a pair of 6L6s for the output to handle the full range and girth of the keyboard. This will give roughly 40 watts of output power, which doesn't sound like a lot compared to many SS keyboard amps, but should be plenty for what will be basically a keyboard monitor. You could always double up to 4 6L6s if you think you will need the extra wattage, but it won't be that much louder. It may give you a more solid low end however.

Moving toward the front end, you'll probably want a flat tonestack that you can boost or cut highs and lows, like a hifi. Most guitar amp tonestacks have a built-in mid-dip which is probably not appropriate for keyboard. There is one, however, that will work. It's called the James tonestack (or sometimes also called the Baxandall tonestack although really they are different). Most James style tonestacks have just the treble and bass controls, but a few add the mid control as well.

You won't need as much voltage gain through the preamp as guitars need so that will simplify and probably reduce the number of preamp tube stages you will need.

For the cabinet (and I'm way out of my depth here) you might consider a wedge shaped design, or a tilt-back design as is common with many bass and keyboard amps currently. I would build it as a ported enclosure. The amp parts I would put in their own section of the enclosure at the top and possibly find a way to vent through the front panel or mount a small muffin fan to dissipate the heat.

Weber has design you could start with that has all of these elements. It's his 6O100 kit. There's a bunch of stuff I'd remove to simplify things for your situation, but the essentials are there.

Hope this helps.....

[Sonny ReVerb]

As far as I know, all kinds are welcome here Welcome!

First, read all the safety documents you can find concerning tube amps. Unlike (most) pedals, these things can KILL you!

That said, you probably can't go wrong with something like a Twin Reverb for keyboards. However, you may want to do a simpler amp to start, to get some experience before diving in to a bigger build. You could always build a simple single channel, single ended amp and give it to a guitar playing buddy There are many places that sell kits, which helps a lot. Mission, Weber, Mojo, etc. I'd start (where I did) over at AX84. They have many beginner to intermediate projects. Be sure to check out the P1 Theory document. It explains a lot of basic concepts.

Be sure to come back with any questions. There are some really knowledgeable folks here, present company excepted.

[Jana]

Other posters are correct in that you should build a small, simple amp first to learn on. Then, if it was me, I would build a 100 watt plexi head. There are only a few minor tweaks in it to change it to the organ model if so desired. I would look at the kits from Metro Amp.

I beg to differ with the thought that you need a hi-fi like setup. If that is the goal, then just run it though a PA. On the other hand, listen to Jon Lord of Deep Purple fame. Although Ritchie would probably say otherwise, and I do love his tone and style, Jon Lord was the centerpiece of that band's sound with that smoking organ sound. Marshall heads and 4*12 cabinets!

[JoeMorris]

Thanks for the tips people.
This won't primarily be for live use, more for studio purposes by the way.. though being suitable for small live gigs would be a bonus.

With this in mind, I would be looking for something to colour the sound to a fair degree rather than a transparent response - something to turn my synths into squealing, dirty leads that I can record through some nice mic setups.... mono is absolutely fine.

[Structo]

Do you like John Lord's B3 tone?

What Marshall was that he used? A JCM 800?

I loved the sound of his organ with Deep Purple.

[dartanion]

Back in the day, keyboard players used what was available to them. For extended low end and clean power, lots used 100W - 200W tube PA heads into various cabinets. For home studio/small gig situations, you would need something with extended low end, so consider using a bass preamp and HiFi type output transformer. Coloring the tone is so subjective, so you'd need to elaborate on your goals for this amp. The biggest concern to me would be that a guitar amp without sufficient output power will be flubby/farty when playing in the lower registers.

FWIW, I have used my old trusty SFTR for keyboards many times and it sounds very nice, although it even gets a bit too loose in the low end if you are playing at high volumes. Not an issue with a guitar.

[Structo]

Yes, I suppose the extended range of a keyboard would be a challenge for most guitar amps, especially the low end.

So Dartanian may be spot on with using a bass spec'd amp.
Maybe a 100 watt Super Bass would be more appropriate.

Funny that the OP seems to want that coloring rather than a straight keyboard amp that generally is clean and adds no additional tone coloring.

I would think depending on the keyboard being used that you could edit the patches to achieve whatever tone you want, regardless of the amp.

You may want to check into the Metro line of amps. By all accounts they are wonderful Marshall clones and many opine a better amp than a Marshall.

You can buy kits of most the older desirable amps.

http://metroamp.com/store/index.php?cPa ... olef6vsrc1

Don't let the specs fool you, you can change the amps to bass specs with just a few component changes and add filtering to help stiffen the bottom end.

[gldtp99]

The Weber schematic/kit linked to is a close copy of an early 70's Orange circuit----except with smaller iron (Marshall 100 watt-sized) and so the Weber is 100 watts vs the orig Orange's 120 watts (conservative).
This circuit is capable of some serious distortion when cranked up but is extremely loud by that point.
Orange also built 80 watt versions with only two EL34 output tubes that distort at somewhat lower vol levels----i've got a '74 Orange OR80 and i've built a copy with modifications for guitar use.
A local keyboard player has demo'd one of my Sound City 120/Hiwatt conversion heads with his keyboard rig--- he used effect pedals of different types to color the sound----- the biggest problem that day was that my Marshall 4x12 cab wasn't able to handle the low freq's that his rig produced---i suspect that a true PA speaker rig (like a 3-way w/crossovers) would be a much better idea.
The Hiwatt circuit was designed to be an "All Purpose" tube amplifier and so it is suitable for guitar, bass, keyboards, PA use-- it is more Hi-fi than most other guitar amps---- the 100 watt version stays cleaner longer than the 50 watt version, not unlike the 120 vs. 80 watt Orange circuits.
If more distortion is required then a Marshall JCM 800 2203 circuit is another great possibility----- 100 watts with EL34's or 6550's---- cascaded preamp design with a Master Vol---i've got a '77 JMP 2203 that is brutally loud after @2 on the MV---these amps also have Hi/Lo inputs so the amount of distortion is adjustable over a wide range. The 50 watt version is the Model 2204---- this is my all-time favorite guitar circuit along with 50's and 60's Fenders.....................gldtp99

[M Fowler]

Welcome,

I have always used bass amps for organ amps, nice clean preamp with clean power section. If you pick a bass tube amp that has the slide EQ section that is a bonus. Also besides the 15 inch woofer a tweater is needed as well.

This is premature but if you decide to build a amp and want it in a floor monitor type of enclosure I have a speaker manual from Peavey from over 20 years ago that has about three different plans to build a 1-12, 1-15 and 2-15 monitor I believe. Been a while since I reviewed it.

Mark

[MBD115]

Many years ago I played keyboard and I usually used a simple bass amp with 2x2x15" speaker cabs with good results. I have a Metro JTM45 build and I must say I don't believe it would make a good keyboard amp (IMO). The tone is colored, which I don't think I would want for a keyboard. For a guitar it is one great sounding amp (again IMO) but I remember liking my keyboard amps to be just an non-colored great sounding amp with a wide freq response, and those two 2x15" speaker cabs I had back then sounded really great. That big bass head had a bunch of clean headroom and would get as loud as i needed it to get without adding distortion on its own. It was a somewhat modified Traynor head and it made me a good amp back then.

Sorry, but I just had to throw in my .o2$

Good luck man!!!!!